Nervous System

Hazel Anne L. Tabo

Nervous System

• Important in transmission of nerve impulses to coordinate the wholistic response coming from the impulse perceived by the body.

• Neurotransmitters – chemical messengers that is transmitted between neuronal cells.

• In the response: Stimuli Afferent (sensory) nerve Center (spinal cord, brain) Motor (efferent) nerve Target organ

Nervous tissue

• Can be organized by anatomical and functional divisions.

• Anatomical Divisions:1. Central nervous system2. Peripheral nervous system

• Functional Divisions1. Sensory component (impulse towards to CNS)2. Motor component (impulse from CNS to effector or

target organs)2.1 – Somatic nervous system2.2 – Autonomic nervous system (sympathetic and parasympathetic)

Anatomical Division

• Central nervous system (CNS)– Includes Brain and Spinal cord (SC)

• Peripheral nervous system (PNS)– Includes nerves outside CNS and associated

ganglia.

Cells of Nervous Tissue

• Neuron structurea. Neuronal cell body (soma/perikaryon) –

contains nucleus, cytoplasmic organelles, inclusions and cytoskeletons.

- Nucleus – aggregates of cell bodies in the CNS (do not confuse it with the nucleus organelle!)

- Ganglion – cell bodies in the PNSb. Dendritesc. Axons

• Neuroglial cells – supporting cells located in the CNS• Schwann cells – neuroglia-equivalent in the PNS

The Neuron• Cell Body / Soma / Perikaryon• 1) Nucleus – centrally located in the soma of most neurons;

euchromatin and dark nucleolus (“owl-eyed nucleus”)• 2) Cytoplasmic organelles and inclusions:

– Nissl bodies – dark clumps in the cytoplasm made of polysomes and rough ER

– Cytoskeletons: neurofilaments (regulates neuronal axon diameter); microtubules (in cytoplasm); microfilaments (in plasma membrane)

• Dendrites – receive stimuli (signals) from adjacent sensory cells, axons or other neurons and converted into electrical impulse; abundant mitochondria.

• Axons – conduct impulses away from the soma and sends it to effector/target organs or adjacent nervous tissue.– Axon hillock – specialized area of soma with high neurofilaments– Axoplasm (axon cytoplasm) – contains sER, rER and long

mitochondria– Axolemma – plasma membrane of axon– Axon terminals – ends of axon

• Electrical Impulse runs through:

• Synapse are functional sites where electrical signals are transmitted from 1 neuron to another or to another target cell (myofiber).

• Dendritic spines increase surface area for synapse formation with other neurons

• Terminal buttons – structure in the ends of axon terminal; form synapse to another cell or dendrite.

• Example of a neuron: Multipolar neuron

http://education.vetmed.vt.edu/Curriculum/VM8054/Labs/Lab9/lab9.htm#

Types of Neuron• Unipolar – one dendrite• Bipolar – two dendrites• Multipolar – multiple dendrites• Pseudounipolar – looks like multipolar but unipolar

• Functional types – responds to chemical transmitters (neurotransmitter)

• Excitatory neuron• Inhibitory neuron• Neurotransmitters – chemical messengers that may promote

or inhibit a certain neural response (impulse).• Ex: Acetylcholine – presents in the myoneural junctions

(neuromuscular junctions). Dopamine, Serotonin, GABA

Neuroglial cells

• Supporting cells of CNS

• Small-sized and numerous than neuron; origin: neural crest cells

• Support, nourishes and protect neurons

• Types: astrocytes, oligodendrocytes, microglia, ependymal cells, Schwann cells

• Astrocytes – largest neuroglial cell; contain many processes forming pedicels (vascular feet) around a blood capillary forming the “blood-brain barrier”; scavenges ion and debris from neuron metabolism and supplies energy for metabolism; support and protects nervous tissue; forms “scar tissue” after injury to CNS.

http://www.kumc.edu/instruction/medicine/anatomy/histoweb/nervous/large/Nerve15.JPG

• Oligodendrocytes – have small, round, condensed nucleus that lives symbiotically with neurons; necessary for neuron survival; produces myelin in CNS; present in CNS gray and white matter.

http://www.microscopy-uk.org.uk/mag/imgapr03/HistPaper03_Fig3a.jpg

• Microglia – small, phagocytotic neuroglial cell that arised from monocytes in the bone marrow; they become APCs (antigen-presenting cell) in the CNS tissue when activated by trapped foreign bodies.

• Ependymal cells – epithelial cells that line the neural tube and ventricles of the brain; they have cilia that aids in moving the CSF (cerebrospinal fluid); cells of the choroid plexus (CSF production)

http://biology.clc.uc.edu/fankhauser/Labs/Anatomy_&_Physiology/A&P202/CNS_Histology/Spinal_Cord/sp_cd_jpgs/Spinal_Cord_PC271498_lbd.JPG; http://www.lab.anhb.uwa.edu.au/mb140/corepages/nervous/Images/epen100he.jpg

• Schwann cells – the only neuroglial cell-equivalent in the PNS; function is similar with oligodendrocytes to produce myelin, the myelin sheath consists of several Schwann cell plasmalemma.

Myelinated nerve fibers – faster impulse conduction

Unmyelinated fibers – slower conduction

• Schwann cell – triangles• Axon - arrows

Peripheral Nervous System

• Branches from the spinal cord• Spinal nerves, Ganglion, peripheral nerves• Nerve fiber – individual axons enveloped by myelin

sheath• Myelin sheath – insulator of heat, myelinated fibers have

higher firing rate, than unmyelinated fibers. It is interrupted by nodes of Ranvier (saltatory conduction) along an axon, these gaps are produced by adjacent Schwann cells.

• Nerves – bundles of nerve fibers; appear whitish due to (+) myelin; CT wrappings

• Ganglia – encapsulated aggregations of soma or cell bodies

Peripheral Nervous System

Connective tissue wrappings of Peripheral Nerve

• Epineurium – covers the whole nerve bundle that forms external coat of nerves formed by dense CT(fascia).

• Perineurium – surrounds each nerve bundle (fascicle); flattened cells are joined by tight junctions (z. occludens) prohibiting passage of macromolecules.

• Endoneurium – forms a thin layer of reticular fibers produced by Schwann cells that surrounds individual nerve fibers (neurofiber).

Central Nervous System

• Brain and Spinal Cord• Matter: Gray Matter and White Matter• Gray Matter (GM) – neuronal cell bodies

(nucleus), more neuroglial cells and many unmyelinated fibers

• White Matter – mostly myelinated fibers and some neuroglial cells

• Brain GM – cortex; WM – medulla• Spinal cord WM – cortex; GM – medulla (H-

section)

Brain, Frontal section

Spinal cord section

• Dura mater – connected to the endosteum of the skull

• Arachnoid mater – sublayer between periosteum and brain, contains network (cobweb) of blood vessels.

• Pia mater – covers the brain parenchyma

Meninges

Skin Sensory Receptors

• Merkel’s disks – free nerve endings (unencapsulated), unmyelinated nerve fibers (skin: stratum basale)

• Meissner’s corpuscle – sensitive to light touch (skin dermis)

• Pacinian corpuscle – deep pressure or coarse touch (skin dermis)

• End bulb of Krause – sensitive to cold (oropharynx lining & eye conjunctiva)

• Ruffinian corpuscle – sensitive to heat (soles of feet)

• Da Lamarcke’s theory of use and disuse can be associated with microcephaly. Such condition may happen if you don’t exercise your brain!